Dioxins formed by normal combustion
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Chlorinated dioxins are naturally formed in minute amounts by normal combustion processes, according to Dow Chemical. Dow scientists have found the compounds, including the highly toxic 2,3,7,8-tetradichlorodibenzo-p-dioxin (2,3,7,8-TCDD), in particulate matter from a variety of combustion sources. In addition, the company says, it has detected dioxins in soil samples. Dow has been on a "crash" program to find sources of 2,3,7,8-TCDD and other dioxins since last summer, when it discovered that the compound was present at parts-per-billion levels in fish taken from the Tittabawassee River. The Tittabawassee flows by Dow's Midland, Mich., plant. And chlorinated dioxins are unavoidably formed in the production of several chemicals, including trichlorophenol, pentachlorophenol, and 2,4,5-T, all of which are made at the Midland plant. Naturally, the plant was suspect. However, Dow says, it has been unable to find dioxins in measurable amounts in effluent water or air from any other specified operations. If the dioxins in the fish didn't come from the plant, where then? To find out, Dow organized a "chlorinated dioxin task force," headed by Dr. Robert R. Bumb, director of R&D at Dow's Michigan division. The group gathered samples from the stacks of refuse incinerators, chemical tar burners, and fossil-fueled power plants; from the mufflers of autos and trucks; from fireplace chimneys; from cigarette smoke; and even from charcoal-broiled steaks. "Chlorinated dioxins were found in every sample of particulate matter taken from the air emissions of a wide variety of commercial and domestic combustion processes," Dow says. Proper combustion can minimize the formation of dioxins, the company adds, but it probably isn't possible to eliminate them entirely. The task force also detected dioxins in soil samples taken in several cities. Dow concludes that particulate matter from combustion processes is an important source of dioxins in the environment. But it emphasizes that the new findings are not cause for alarm. "We now think dioxins have been with us since the advent of fire," Bumb says. "The only thing that's different is our new-found ability to detect them in the environment." Dioxins can be detected at the partsper-trillion level using gas chromatography and high-resolution mass I
spectrometry. To find them in the environmental samples, however, Dow had to develop complicated sample preparation procedures to remove other compounds (present in much larger amounts) that would otherwise interfere with the detection of dioxin. The Dow findings are only the beginning, Bumb says. Refuse and fossil fuels are an extremely complex mixture, he explains, with an enormous number of elements and compounds present at low concentrations. Conditions in a flame favor all kinds of chemical reactions. Heretofore, the "trace reactions" have been largely unstudied, because the necessary measurement techniques weren't available. But with newly developed analytical procedures, it now can be shown that chemicals at parts-perbillion levels can produce measurable amounts of other chemicals. According to Bumb, the dioxin discoveries open up a whole new field: the study of the trace chemistry of fire. •
Debate renewed over ethylene dihalides The debate on the cancer-causing potential of ethylene dihalides (dihaloethanes) is heating up further. The latest questions arise from publication of final results of tests sponsored by the National Cancer Institute showing strong carcinogenesis of ethylene dibromide fed through tubes into rat and mice stomachs (C&EN, Nov. 13, page 17). The manner of the disclosure and the reaction to it from chemical firms producing ethylene dibromide are strikingly similar to what happened two months ago when NCI issued results of tests showing carcinogenesis of ethylene dichloride ingested by rats and mice. Both sets of tests were run by Hazleton Laboratories America in Vienna, Va. Both disclosures seem to confirm earlier results. About both NCI reports, industry is asking why now, and so what. Large-dosage, direct feeding tests on animals are unacceptable to companies, which maintain that proper test procedure would be inhalation tests, as these are more like actual human exposure conditions. The commercial stakes in ethylene dibromide are less than a tenth as high in volume or value as industry's vested position in ethylene dichloride, the precursor to polyvinyl chloride. Nevertheless, ethylene dibromide is the leading bromine-based chemical, with U.S. production at 244 million lb in 1977, according to the International Trade Commission. At long-
Ethylene dibromide at a glance U.S« production: 244 million fb In 1977, down 32% from peak 332 million lb in 1974 U.S. producers: Dow Chemical, Ethyl Corp., Great Lakes Chemical, PPG Industries Markets: Lead scavenger in gasoline 90%; other, including pesticides and intermediates in dyes and drugs, 10% Price: 37 cents a lb in drums Market value: $80 million in 1977 for total production Outlook: Sharp decline in demand, possibly 75%, by 1980 due to phasedown of lead additives \n gasoline and possible restriction of use in pesticides
time steady prices, this volume is worth about $80 million. Ethylene dibromide demand is already in sharp decline, because 90% of its market is tied to the use of lead additives in gasoline, a use that has been declining. Ethylene dibromide is used as a scavenger to convert lead oxides in automobile and other engines to lead halides, which escape with engine exhaust. Hence, the NCI test results amount largely to another nail in the coffin. Even though ethylene dibromide producers—Dow Chemical, Ethyl Corp., Great Lakes Chemical, and PPG Industries—have long known of its uncertain future, they have stepped up investment in bromine chemicals during recent years. The reasoning is that bromine has promise in other markets such as flame retardants and water conditioners. Apparently, bromine chemicals have yet to suffer as a whole from the declining use of ethylene dibromide. The company with the biggest stake in bromine chemicals relative to total sales, Great Lakes Chemical, is chalking up another good year in 1978 with earnings up 16% over 1977 through three quarters. Reacting to the current NCI test results, Dow says that the disclosure has caused an unnecessary stir. It sees little difference from similar test results by NCI first published in December 1973. Dow continues to maintain that it is hard to extrapolate results of gross stomach exposure to ethylene dibromide in rats to inhalation exposure in humans. It says that epidemiological surveys on employees at two Dow ethylene dibromide plants show no increased incidence of cancer over incidence in the general • I population. Nov. 20, 1978 C&EN
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